1. Field of the Invention
The present invention relates to a zoom lens system and an apparatus such as an electronic image pickup apparatus using the zoom lens system.
2. Description of the Related Art
Instead of a 35 mm film still camera, a digital camera has broadly spread, and the digital camera has a large number of categories in a broad range from a multi-function type for business use to a portable popular type. The present invention especially pays attention to the portable popular type of category, and aims to provide a technology of realizing a thin video camera and/or a thin digital camera while securing high image qualities.
Thinning of the camera in a depth direction is hampered most by a thickness of an optical system, especially the thickness of a zoom lens system from the surface closest to an object side to an image pickup surface. In recent years, it has been a mainstream to use a so-called collapsible lens barrel so that the optical system is projected from a camera body during photographing and stored in the camera body during carrying. Furthermore, to satisfy a demand that a user desires to enjoy a wide variety of photographing, a zoom lens system having a large angle of field in a wide-angle end and having a high zoom ratio is demanded. In Japanese Patent Application Laid-Open No. 2003-255228, there is disclosed a zoom lens system having a zoom ratio which is as large as about fivefold and having an angle of field which is as large as about 60° in the wide-angle end. In the zoom lens system, a position of an exit pupil is appropriately set. The zoom lens system is suitable for an electronic image sensor, and has a comparatively satisfactory optical performance.
The zoom lens system described in the above publication is a five-unit zoom lens system having a power layout of a positive, negative, positive, negative and positive type. The zoom lens system is advantageous in securing the zoom ratio and satisfactorily correcting aberrations.